New Jersey Gov. Chris Christie and his wife Mary Pat Christie look over the podium during a sound check the Republican National Convention in Tampa, Fla., on Tuesday, Aug. 28, 2012. (AP Photo/Charles Dharapak)

TAMPA, Fla. (AP) — Blunt and brash, New Jersey Gov. Chris Christie would seem the perfect Republican to skewer President Barack Obama and fire up thousands of GOP loyalists.

That's exactly what he was expected to do late Tuesday when he delivers the keynote address before the Republican National Convention.

His mission: making the case against Obama.

Christie's outspoken style has made him a Republican Party star and helped earn him the plum, prime-time speaking spot.

He rocketed to GOP stardom in 2009, winning the Democratic-heavy Eastern state the year after Obama was elected and establishing a reputation as confrontational to big labor and public employees.

Indeed, early in last year's GOP nominating campaign, Republicans uninspired by Romney aggressively urged Christie to seek the nomination.

New York delegate David Shimkin said he admired Christie's frankness.

"He doesn't seem to have a filter. A lot of candidates don't do that," Shimkin said of Christie.

As keynote speaker, Christie is tasked with making the opening pitch for presidential candidate Mitt Romney, who remains something of a mystery to voters even though polls show him locked in a close contest with Obama.

Christie considered running for the nomination himself but months ago decided to endorse Romney, who made a personal entreaty for Christie's support as the GOP primaries were getting under way.

Christie on Tuesday waved off a published report that he had turned down an offer to be Romney's running mate because he didn't think Romney could win in November.

"Not only do I believe he can win, I think he will win," Christie told "CBS This Morning."

Temperamentally and stylistically the opposite of the buttoned-up Romney, Christie acknowledged the former Massachusetts governor has work to do to close the sale with some voters, especially women.

"Mitt Romney's going to have to win this campaign. He's going to have to let the American people see who he is," Christie said on ABC's "Good Morning America," adding that Romney's choice of Paul Ryan as his running mate had brought more energy to the ticket.

After toppling Democratic Gov. Jon Corzine in 2009, national Republicans embraced Christie for his tough talk on fiscal matters and for taking on public employee unions, especially teachers. Videos of Christie berating teachers at town hall meetings quickly went viral, giving Christie a large national audience. Critics dubbed him "Governor YouTube," suggesting he was more interested in getting publicity for himself than for improving New Jersey's finances.

Christie has disclosed little about he will say in the speech, but said it would include a discussion of "the New Jersey experience and what the experience might mean for the country in terms of governing and hard choices."

That drew a jeer from Democrats, who said viewers shouldn't buy Christie's claim of a "Jersey comeback." They pointed to economic data showing the state still grappling with weak employment and high property taxes.

"Chris Christie is taking the stage in Tampa tonight to talk about his favorite topic: himself," state Assemblyman John Wisniewski told reporters during a conference call. "Gov. Christie's record in New Jersey is certainly not a model for our nation, and the people in Tampa should know that."

Maryland Gov. Martin O'Malley, chairman of the Democratic Governors Association and a likely 2016 presidential contender, went further, saying he expected Christie to deliver an "angry, Don Rickles keynote extolling the virtues of their candidate, Mitt Romney, who had one of the worst job creation rates in the nation."

Christie is popular among convention delegates, many of whom said they would have welcomed a Christie presidential candidacy.